1. Field of the Invention
The field of the present invention is apparatus and methods for producing heat exchange with a body fluid flowing through a body conduit of a patient.
2. Description of Related Art
Catheters such as central venous line catheters are typically used in ICU (intensive care unit) patients, particularly in those patients who have suffered a stroke or other brain traumatic event. Central venous line catheters are typically about 5 to 12 French in size and have a flexible multi-lumen elongated body extending 6 to 12 inches. They may be introduced through the subclavian or jugular veins, or through the femoral vein of the patient, serving to provide the caretaker with easy and convenient access to the patient""s central blood supply via the central venous system. In this manner general access to the central blood supply is gained, enabling, for example, delivery of drugs, infusion fluids or nutrition, along with the gathering of patient blood for blood gas analysis and the like.
In certain medical circumstances, such as in the case of a stroke patient or other brain trauma patient, it may be desirable to rapidly reduce the patient""s body temperature. For example, fever, which is common in neuro-ICU patients, may exacerbate detrimental effects in the brain. It may be desirable to reduce the body temperature of a patient having a fever to a normal body temperature. In other cases, it is sometimes considered desirable to reduce the patient""s body temperature below normal body temperature so that the patient experiences hypothermia. Many advantages of hypothermia are known. By way of example, it has been found desirable to lower the temperature of body tissue in order to reduce the metabolism of the body. This has been particularly desirable in surgical applications where the reduced metabolism has made it possible to more easily accommodate lengthy operative procedures. In cases of stroke and several other pathological conditions, hypothermia also reduces the permeability of the blood/brain barrier. It inhibits release of damaging neurotransmitters and also inhibits calcium-mediated effects. Hypothermia also inhibits brain edema and lowers intracranial pressure.
Conventional therapies to cool a patient include treatment with acetaminophen (Tylenol), cooling blankets, ice water bladder lavages, and ice baths. These approaches to cooling a patient require excessive cooling time and do not provide for precise control of patient cooling.
In other medical situations, it may be desirable to raise the patient""s body temperature. For example, a patient may suffer from unintended hypothermis and may need to be warmed to a normothermic temperature, e.g., 98.6xc2x0 F. These results can be obtained by intravascular heating.
In order to minimize the number of incisions and catheter insertions into the patient""s body and cool or heat the patient relatively quickly and in a controlled fashion, an infusion catheter may be configured to include a heat exchange capability.
By supplementing the known functions of a central venous line catheter with the function of cooling or warming the patient""s blood, a catheter may take advantage of existing access to the venous system using a single, relatively small incision, reducing the risk of additional complications. The access, typically through the subclavian, jugular or femoral veins, is to the central blood supply, via the central venous system, and is therefore particularly expedient, permitting efficient cooling or warming of a patient. The term central venous system generally relates to the portion of the venous system which returns blood to the right side of the heart, including the inferior and superior vena cava.
An infusion catheter having one or more lumens may be inserted into a blood vessel of a patient to deliver medication, collect blood for analysis, and the like. A separate lumen may be provided for transporting a heat exchange fluid, e.g., cold or hot water or saline. The fluid may circulate via the lumen and through a thin-walled inflated balloon formed on the surface of the catheter. The fluid exchanges heat with the blood in the blood vessel via the thin walls of the balloon. Outside the patient""s body, the fluid passes through a cooling or heating system to re-cool or re-heat the fluid. Such a catheter may lower or raise the temperature of the patient""s blood and, as described above, may thereby improve the patient""s medical condition.
It would be advantageous to provide a central venous catheter with the capability of maximizing cooling or heating of a patient safely and in a controlled manner. The rate of heat transfer depends on such factors as the volumetric flow rates of the blood and the heat exchange fluid, and the temperature difference between the heat exhcanger and the blood. Other factors include the convection heat transfer coefficient of the two fluids involved in the heat exchange, the thermal conductivity and thickness of the barrier between the two fluids, and the residence time of the heat transfer. Increasing the cooling or heating rate may be accomplished by, for example, increasing the size (diameter and/or length) of the balloon, or increasing the temperature difference between the heat exchange fluid and the blood.
Increasing the diameter of the balloon, however, may result in blocking the flow of blood in the blood vessel, and/or may cause thrombosis. Increasing the size of the balloon is further complicated by the fact that the size of blood vessels may vary widely among different patients. A catheter that maximizes heat transfer for a larger patient may be too large for use in a smaller patient, and a catheter that maximizes heat transfer for a smaller patient may not maximize heat transfer in a larger patient. For example, a relatively large balloon, when inflated, may excessively block blood flow through a smaller patient""s blood vessel, increasing the risk of thrombosis. Further, a tip of a relatively large catheter designed for a larger patient, if inserted completely into a smaller patient""s upper central venous system, may extend into the patient""s heart.
Increasing the temperature difference between the heat exchange fluid and the blood excessively may lead to undesireable effects, such as thermal damage to the blood vessel wall. Further, blood has a maximum desirable heating limit because above certain termperatures blood proteins may degenerate and coagulation may occur. This limits the maximum operating temperature of known intravascular catheters.
The rate of heat transfer may also depend partially on the geometry of the heat exchanger. Because the operating temperature of an intravascular catheter is limited, the catheter geometry may take on increased importance to effectuate heat transfer. The flow of the heat exchange fluid inside the balloons may be non-laminar, and the flow of the patient""s blood over the balloons may also be non-laminar, such that much of the heat exchange occurs between only portions of the heat exchange fluid and blood that are nearest the balloon surfaces. To promote mixing or disturbance of the flow paths of the heat exchange fluid and the patient""s blood, the balloons may be configured in helical (referred to interchangeably herein as xe2x80x9cspiralxe2x80x9d) shapes, or otherwise configured, such that the flow of the heat exchange fluid and the blood is non-laminar, increasing the rate of heat transfer.
It would be advantageous to provide a heat exchange catheter that maximizes intravascular cooling and heating without comprising physiological conditions, and facilitates access to the patient""s blood stream, thereby overcoming one or more problems associated with the related art.
The present invention is directed to a heat exchange catheter and method for its use. A heat exchange element or elements is combined with an infusion lumen or lumens to provide efficient cooling (and/or heating) and access to the patient""s blood steam.
In a first separate aspect of the invention, a heat exchange catheter comprises a generally tubular elongated body defining an inflow lumen, an outflow lumen, and at least one infusion lumen. The inflow and outflow lumens circulate heat exchange fluid within a plurality of heat exchange elements disposed about a distal, implantable portion of the catheter; while the infusion lumen serves to provide access to the central blood supply of the patient.
In a second separate aspect of the invention, a heat exchange catheter has a cross-sectional size such that no more than approximately 30% to 75% of the cross-section of a blood vessel in which the catheter is inserted is blocked by the catheter.
In a third separate aspect of the invention, one or more heat exchange elements is disposed over a particular length of the elongated body such that the heat exchange elements the maximize heat transfer rate without harming the patient.
In a fourth separate aspect of the invention, a heat exchange catheter may be inserted into a patient""s central venous system through the patient""s femoral vein.
In a fifth separate aspect of the invention, a heat exchange catheter is provided with multiple infusion lumens (preferably three to five infusion lumens) with infusion ducts separated along the catheter at spaced intervals, such that the catheter may be used to simultaneously introduce various fluids, such as medications, into the patient at different points in the patient""s blood stream, so as to avoid mixing incompatible fluids in excessive concentrations.
In a sixth separate aspect of the invention, a heat exchange catheter is provided with multiple balloons (preferably three or four balloons) that are spaced along the elongated body to provide controlled and balanced heat transfer, with a gap between balloons to provide the catheter with flexibility.
In a seventh separate aspect of the invention, a heat exchange catheter is provided with gaps between multiple balloons, so that an infusion duct may be disposed in each gap.
In an eighth separate aspect of the present invention, it is contemplated that combinations of the foregoing separate aspects may be incorporated into a single embodiment.
Therefore, it is an object of the present invention to provide an improved heat exchange catheter and a method for its use. Other and further objects and advantages will appear hereafter.